1. Field of the Invention
The present invention provides a light source system for a projection apparatus, and in particular, to a hybrid light source system for a projection apparatus.
2. Descriptions of the Related Art
With the widespread use of projection apparatuses, the competition in the projection apparatus market has also become increasingly intensified. Under such circumstances, manufacturers must make great efforts in improving the quality of existing projection apparatuses to satisfy the demands of users and attract more consumers. For example, projecting an image with a wide color gamut to make the image close to the true color is an important factor in attracting consumers.
As can be known from conventional technologies, among the primary colors of projection apparatuses, the color red has the most prominent effect on imaging quality. Therefore, in a conventional projection apparatus 1 as shown in FIG. 1, a red laser 11 is used as a light source in addition to an ultra high pressure (UHP) lamp 12. This is because the laser provides light that has relatively concentrated frequencies and pure colors, and after the laser light is mixed with the light from the UHP lamp 12, colors of a wide gamut can be provided. According to the basic principles of optics, to avoid increasing the etendue in the conventional projection apparatus 1, light emitted from the red laser 11 and the UHP lamp 12, after travelling through the lens modules 13, 14 respectively, must transmit through a dichroic filter 15 to form a hybrid light source before entering the imaging system 16 for imaging. In this way, the light can be utilized more effectively. It should be appreciated that the arrowed lines in this figure are only used to schematically illustrate the primary light path.
In this projection apparatus, the red laser 11 and the UHP 12 project light towards the dichroic filter 15 at an angle of 45° respectively. The dichroic filter 15, with a film (not shown) coated thereon, allows the red laser beams emitted from the red laser 11 to pass therethrough, but reflects a portion of the light beams emitted from the UHP 12. With this arrangement, a portion of the light emitted from the UHP 12 that is in the same range of spectrum as the red light emitted from the red laser 11 will also travel through the dichroic filter 15. As can be known by those of ordinary skill in the art, the dichroic filter 15 is adapted to allow light beams within a predetermined spectrum range to pass therethrough due to the coating film thereof; additionally, the dichroic filter 15 results in a dichroic shift characteristic depending on the different incident angles of the light beams. More specifically, with the larger incident angle of a light beam, the dichroic shift will shift towards a shorter spectrum; i.e., as the incident angle increases, the spectrum of the light beam that is allowed to pass through the dichroic filter 15 becomes shorter. For example, the light beams provided by the UHP 12 and the laser 11 in FIG. 1 are incident to the dichroic filter 15 substantially at an angle approximately ranging from 41° to 49°. According to the aforesaid dichroic shift characteristic, as shown in FIG. 2 where the vertical axis represents the light transmittance and the horizontal axis represents the wavelength, light beams incident to the dichroic filter 15 at different incident angles (e.g., 41°, 45°, 49°) will produce a shifted dichroic curve respectively. The curve indicated by the triangular symbols represents a dichroic curve corresponding to the incident angle of 49°, the smooth curve represents a dichroic curve corresponding to the incident angle of 45°, and the curve indicated by the circular symbols represents a dichroic curve corresponding to the incident angle of 41°. For the light beams emitted from the red laser 11 to completely transmit through the dichroic filter 15 in response to the light beams emitted from the UHP 12 that are incident on the dichroic filter 15 at different incident angles, the dichroic filter 15 must be designed to allow a larger range of light spectrum to pass therethrough. Thus, the light beams emitted from the red laser, of which the spectrum is as shown by the rectangle in FIG. 2 (near the wavelength of 640 nm), can still be included in the transmittable range of spectrum (as encircled by the dashed line) with the dichroic shift. However, a larger transmittable range of spectrum also means that the light beams emitted from the UHP lamp 12 will be transmitted through the dichroic filter 15 accordingly and will lead to a significantly degradation of light intensity intended for imaging, which is very unfavorable for the imaging quality.
In view of this, it is highly desirable in the art to mitigate the dichroic shift effect so that the brightness as well as the color gamut of images can be enhanced by the efficient use of the light.